The invention may be applied, notably, to the voltage control of an apparatus by pulse width modulated signals, referred to in English as “PWM” or “pulse width modulation” signals.
In a motor vehicle, some apparatuses are controlled in a known way by a control unit, using pulse width modulated voltage control signals (PWM signals). The apparatus may be, for example, an ignition coil, a fuel injector, a fuel pump, an idle valve, or the like.
Pulse width modulation is a commonly used technique for synthesizing continuous signals using circuits with on/off operation, or more generally circuits having discrete states. The general principle is that, by applying a sequence of discrete states during carefully selected time intervals, any intermediate value may be obtained on average over a given time interval.
A voltage-controlled apparatus may be modeled in a known way by an RLC circuit which is electrically connected to the vehicle battery on one hand, and to the ground on the other hand, and which comprises a first branch composed of a capacitor, in parallel with a second branch composed of a resistor and an induction coil connected in series.
The pulse width of the signals for controlling the voltage of the apparatus is predetermined in a known way, for example by the manufacturer, on the basis of this modeling and notably on the basis of the theoretical values of resistance, inductance and capacitance of the model equivalent to the apparatus.
However, it may be the case that this value is unsuitable for controlling the apparatus, for example because the manufacturer's specifications are incorrect in relation to the model, or because the electrical connection between the control unit and the apparatus creates losses which modify the RLC circuit model, or because the resistance, inductance and capacitance values of the model drift over time.
Controlling the voltage by signals of incorrect width may result in an excessively strong or weak input current, which may eventually damage the apparatus, and therefore constitutes a serious drawback.